Weight as an indicator of enclosure suitability in Livingstone's fruit bats (Pteropus livingstonii)

Abstract

Obesity is common in zoo animals, and both dietary management and the provision of adequate opportunities for exercise are needed to tackle it. We used 30 years of records from Jersey Zoo to compare the weight and forearm length of wild and captive‐born Livingstone's fruit bats (Pteropus livingstonii), and to assess the impact on weight of enclosure space. The mean capture weight of wild‐caught male Livingstone's bats was 657 g, significantly higher than that of females (544 g). In both wild and captive‐born bats, males had significantly longer forearms than females, but there was no effect of birth location. Males weighed more in the mating season than at other times of year. Both sexes gained more weight during development if born in enclosures that restricted flight rather than a large aviary; this was particularly noticeable in females. After reaching maturity at 3 years, weights of bats born in restricted enclosures continued to increase, reached a peak of over 1000 g at 8−10 years, and then declined in both sexes. The weight of bats born in the aviary remained more stable after the age of three. Like wild bats, adult females born in the aviary weighed less than males. However, females born in restricted enclosures weighed more than males born in the same enclosures. Enclosure designs that maximize opportunities for flight can limit excessive weight gain in captive fruit bats and may therefore improve fitness and health, essential in planning for future reintroduction programs.

In Absentia—Can a Lack of Behaviour Be a Useful Welfare Indicator? An Application to the Captive Management of Livingstone’s Fruit Bats, Pteropus livingstonii

“…Bats older than ten years old were not observed performing any flying behaviour, possibly due to their dominance rank, which renders them more likely to be sedentary and control a territory [17,27]. It has recently been shown that bats living in smaller enclosures are more likely to have a higher body mass, presumably due to their limited opportunities to fly [16], again supporting our expectation of reduced locomotion correlating with higher body mass. Additionally, reluctance to fly and lethargy are two of the clinical signs of cardiomyopathy in Pteropus species described by Killick et al (2017).…”

“…This would be especially true when subordinates are foraging as they might need to enter a dominant individual's territory; bats that frequently move between social groups are known to have higher cortisol levels in this species, highlighting that perceived levels of risk can be higher in these individuals [30]. Individuals with a larger body mass are likely to be showing reduced vigilance behaviour as they are more likely to be territory holders and therefore hold a higher dominance rank (as body mass, age, and dominance rank are positively correlated in this species; [16,28], with less need to socially monitor others. Particularly low levels of vigilance behaviour could indicate higher body mass in this species, meaning this behaviour could be used by keepers as an indicator of risk of cardiomyopathy; males that are showing low levels of vigilance have more time for foraging and therefore weight gain.…”

“…Accelerometer data gathered on two wild individuals found that P. livingstonii travels on average between 9.5 km and 12.7 km daily [13]. In captivity, allowing individuals the opportunity to be active and maintain adequate fitness levels is essential for their health and potential for reintroduction [11,14,15]; body mass is strongly influenced by enclosure size, and hence opportunities for flight, in this species [16]. However, due to the complexity of Pteropus flight patterns, as described by Bell et al (2019), flight can be highly limited by objects in their enclosure; increasing opportunities for flight in captive fruit bats is therefore not straightforward.…”

“…Males appear to be more prone to cardiomyopathy since older dominant males are more sedentary and defend feeding territories [11], rendering them more at risk of obesity. It is further suggested that older, heavier individuals will struggle to fly in a restricted space, escalating the impact of obesity through reduced activity in a negative feedback loop [11,16]. While certain clinical signs, such as increased respiration rate, effort, and reduced activity, are attributable to cardiomyopathy, these often arise once the disease has progressed too far to effectively treat it [19].…”